1. Field of the Invention
The present invention relates to a film-type adhesive for electronic components, which adhesive can be easily and efficiently handled and, when subjected to low-temperature, short-duration treatment, exhibits excellent solvent resistance and excellent adhesion to adherend surfaces of various constructions. The invention relates also to electronic components bonded using such an adhesive.
2. Prior Art
Polyimide resins have excellent heat resistance and electrical insulating properties, and are widely used as adhesives for bonding electronic components. Although they are usually employed in the form of solutions, polyimide resins are soluble only in a limited number of high-boiling solvents. Accordingly, it is common practice to coat the adherend with a solution of polyamic acid, a polyimide precursor which is soluble in a variety of solvents, and carry out extended heat treatment at a temperature of at least 300xc2x0 C. to effect dehydration and imidization. However, such heat treatment may cause heat deterioration of the adherend. On the other hand, insufficient heating may leave residual polyamic acid in the resin layer, lowering the resistance to moisture and corrosion.
In one known method that addresses such problems, a resin film is formed by coating the adherend with a solution of solvent-soluble polyimide, then heating to remove the solvent. However, the resulting resin layer often has a lower solvent resistance.
Because these prior-art methods use the adhesive in the form of a solution, complications are encountered in applying the solution, removing the solvent, and handling of the adhesive in general. Problems arise unless sufficient solvent is removed. Namely, when the adhesive is exposed to elevated temperatures in later operations, as in the case of die bonding materials in semiconductor devices in particular, the residual solvent vaporizes, forming voids, which may cause delamination and cracking.
Therefore, it is an object of the invention to provide a film-type adhesive for electronic components which can be easily and efficiently handled and which, when subjected to low-temperature, short-duration treatment, exhibits excellent solvent resistance and excellent adhesion to adherend surfaces of various constructions. Another object of the invention is to provide electronic components bonded using such an adhesive.
The inventor has found that by dissolving in a solvent a polyimide resin (A) of a specific structure and molecular weight that is composed of repeating units of structural formula (1) below in combination with an epoxy resin (B) having two or more glycidyl groups per molecule, in a weight ratio of component (A) to component (B) within a range of 50/50 to 5/95, and subsequently removing the solvent from the solution to form a film having a thickness of 20 to 150 xcexcm, there can be obtained a highly reliable adhesive for electronic components which is easy and efficient to handle, which resolves such problems as void formation, delamination and cracking on account of residual solvent, and which has excellent solvent resistance and excellent adhesion, even with low-temperature, short-duration treatment, to various types of adherend surfaces, and especially adherends having an irregular surface as well as those having a smooth surface.
Accordingly, the invention provides a film-type adhesive for electronic components that comprises (A) a polyimide resin comprising repeating units of structural formula (1) below and having a weight-average molecular weight of 5,000 to 150,000 and (B) an epoxy resin having at least two glycidyl groups per molecule, which adhesive has a weight ratio of component (A) to component (B) of 50/50 to 5/95 and a film thickness of 20 to 150 xcexcm. 
X is at least one tetravalent organic group selected from the following. 
Y is a divalent organic group composed of 30 to 99 mol % of one or more phenolic hydroxyl group-bearing aromatic diamine residue Y1 selected from among 
and 70 to 1 mol % of one or more aromatic diamine residue Y2 selected from among 
Z is a siloxane diamine residue of the following formula: 
wherein R1 is a substituted or unsubstituted monovalent hydrocarbon group of 1 to 10 carbon atoms, the letter xe2x80x9caxe2x80x9d is an integer from 1 to 6, and b is an integer from 1 to 120.
The letters m and n are positive numbers which satisfy the conditions 0.70xe2x89xa6m/(m+n)xe2x89xa60.98 and 0.02xe2x89xa6n/(m+n)xe2x89xa60.30.